local p = {}
local format = string.format
local gsub = mw.ustring.gsub
local trim = mw.text.trim
local upper = mw.ustring.upper

local prepattern = "%[(%w+)%|(.*)%|(.*)%|(.*)%]"
local pattern = "%%(%w+)%%"

local function parser(formatStr, args, form)
	local function ifexists(name)
		if name == '' then return false end
		local title
		if form == 'shield' then
			title = mw.title.new(name, 'Media')
		else
			title = mw.title.new(name, 0)
		end
		return title.exists
	end
	local function testArgs(test, equals, ifexists, ifnot)
		if equals ~= '' then
			if args[test] == equals then return ifexists else return ifnot end
		else
			if args[test] and args[test] ~= '' then return ifexists else return ifnot end
		end
	end
	local formatTable = {}
	-- Recursively dig into tables that could be parser hooks or argument tables.
	local function formatStrInTable(formatStr)
		if type(formatStr) ~= "table" then return formatStr end
		formatTable = formatStr
		local hook = formatStr.hook
		local both = formatStr[2]
		if both then
			local first = formatStrInTable(formatStr[1])
			local second = formatStrInTable(both)
			return {first, second}
		elseif hook then
			local hooksModule = require "Module:Road data/parser/hooks"
			local hookFunction = hooksModule[hook] or error("Hook '" .. hook .. "' does not exist", 0)
			return formatStrInTable(hookFunction(formatStr, args))
		else
			local arg = args[formatStr.arg or "route"]
			return formatStrInTable(formatStr[arg] or formatStr.default)
		end
	end
	local function parse(formatStr)
		local preprocessed = gsub(formatStr, prepattern, testArgs)
		local parsedStr = gsub(preprocessed, pattern, args)
		local final = trim(parsedStr)
		if formatTable.ifexists then
			local exists = ifexists(final)
			if exists then
				return final
			else
				return parser(formatTable.otherwise, args, form)
			end
		end
		return final
	end
	formatStr = formatStrInTable(formatStr)
	if not formatStr or formatStr == '' then return '' end
	if type(formatStr) == 'table' then
		local first = parse(formatStr[1])
		local second = parse(formatStr[2])
		return first, second
	else
		return parse(formatStr)
	end
end

local function formatString(args, form)
	local function getTypeData(module, type)
		local success, moduleData = pcall(mw.loadData, module)
		if not success then return '' end
		local typeTable = moduleData[type] or moduleData['']
		local defaultTable = moduleData[''] or {}
		if typeTable then
			local alias = typeTable.alias
			if alias then
				local aliasedModule = "Module:Road data/strings/" .. alias.module
				local aliasedType = alias.type
				return getTypeData(aliasedModule, aliasedType)
			end
			return typeTable[form] or defaultTable[form] or ''
		else
			return ''
		end
	end
	
	local stateCountries = {USA = true, CAN = true}
	local state = upper(args.state or '')
	local country
	if args.country then
		country = upper(args.country)
	else
		local countryModule = mw.loadData("Module:Road data/countrymask")
		country = countryModule[state] or 'UNK'
	end
	local typeArg = args.type
	local module
	if stateCountries[country] and state ~= '' then
		module = format("Module:Road data/strings/%s/%s", country, state)
	else
		module = format("Module:Road data/strings/%s", country)
	end
	return getTypeData(module, typeArg)
end

function p.parser(passedArgs, form)
	local args = {state = passedArgs.state, type = passedArgs.type, route = passedArgs.route, 
	              denom = passedArgs.denom, county = passedArgs.county, dab = passedArgs.dab,
	              country = passedArgs.country, township = passedArgs.township}
	local formatStr = formatString(args, form)
	if not formatStr or formatStr == '' then return nil end
	return parser(formatStr, args, form)
end

return p